Pickup unit for cathode plates or the like

ABSTRACT

A unit for lifting groups of workpieces such as cathode plates on suspension bars and transferring them to another location. The unit comprises a rectangular frame with legs straddling the assembled plates. Gates on opposite sides of the frame are swung inwardly to align the suspension bars and the unit is then lifted by a crane, lift bars on the gates carrying the plates upwardly. The unit and its load are moved to another location such as a multi-tiered rack and the plates and suspension bars lowered onto the rack. An actuator carried by the unit engages the bars on the rack as the unit descends to swing open the side gates, and the unit may be returned to the assembly station.

[4 Feb. 19, 1974 9/1952 Jaeger................................. 10/1944 2,610,890 2,360,740 Sturdy PICKUP UNIT FOR CATHODE PLATES OR THE LIKE [75] Inventors: Cass S. Kasper, Grosse Pointe;

Primary Examiner-Evon C. Blunk Vern? Mount Clemens both Assistant Examiner-Johnny D. Cherry of MlCh.

ABSTRACT A unit for lifting groups of workpieces such as cathode [73] Assignee: Inter-Lakes Engineering Company,

Mt. Clemens, Mich.

Apr. 21, 1972 [22] Filed: plates on suspension'bars and transferring them to an- [2l] Appl. No.1 246,341

other location. The unit comprises a rectangular frame with legs straddling the assembled plates. Gates on opposite sides of the frame are swung inwardly to align the suspension bars and the unit is then lifted by a [52] US. 294/67 R, 294/67 BC Int. B66c 1/16 crane, lift bars on the gates carrying the plates upwardly. The unit and its load are moved to another location such as a multi-tiered rack and the plates and suspension bars lowered onto the rack. An actuator carried by the unit engages the bars on the rack as the unit descends to swing open the side gates, and the 294/67 DB unit may be returned to the assembly station.

294/67 DA', 67 DB, 81 R, SLSE [56] References Cited I UNITED STATES PATENTS 1 7 J I.V w WM; LJ S A a llllillllll aw 31 v, a M J. .m I a v. w i W, 5 a a n :fbl l v v 1 n 1 r g fi s nfifil AMA." h CX BF l W m is 4 m 1 1. 2 2 wk 82 .171 "MM NH. M wm. .1 05 m PAIENTEB FEB] 91974 SHEET 3 BF 3 PICKUP UNIT FOR CATHODE PLATES OR THE LIKE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the handling of workpieces such as cathode plates carried by suspension bars. Such assemblies, comprising thin sheets of pure copper suspended by bars secured to their upper edges, are used in the electrolytic refinement of copper. Our copending application Ser. No. 217,782 filed Jan. 14, 1972, describes a machine and process for assembling these cathodes and suspension bars and assembling them in groups at closely spaced intervals on a pair of slide rails. When the cathodesare finally placed between anodes in the electrolytic bath, their spacing is substantially greater than that on the slide rails. For example, the spacing on the slide rails may be one inch whereas the desired final spacing is four inches (two inches between each cathode and its adjacent anodes). It is known to provide this greater'spacing by lifting a group of closely spaced cathode assemblies from the slide rails and lowering them onto a four-tiered rack so that the group is separated into four groups with the spacing in each group being four inches.

2. Description of the Prior Art The presently known means for lifting the groups of cathode assemblies from the slide rails and depositing them on the tiered racks comprises conventional lifting apparatus suspended from a crane. This apparatus requires the presence of several men on the plant floor in addition to thecrane operator so that the equipment may be lined up with the suspension bars on the slide rails, the crane hooked up, and the load properly positioned and lowered onto the multi-tiered rack.

BRIEF SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel and improved means for handling cathode assemblies or the like which will eliminate the need for floor attendants but will permit the crane operator himself to remove successive groups of cathodeassemblies'from the slide rails and place them on a multi-tiered rack in an accurate, efficient and speedy manner.

It is a further object to provide improved apparatus of this type which will automatically align the suspension bars before each group is lifted from the slide rails and insure that the load cannot escape during the transfer operation.

It is a further object to provide a pickup unit of this character which will automatically release itself from the load once it is placed on the rack, so that the unit may be returned to the assembly area in readiness for another load, without the presence of floor personnel.

It is another object to provide a novel and improved handling unit of this type, which is independent of the crane and may remain at rest in readiness for use while the crane is elsewhere.

Briefly, the inventioncomprises a rectangular frame with legs straddling the slide rails, the frame being engageable by crane hooks. A pair of gates are pivoted on opposite sides of the frame and swingable between open and closed positions. Each gate comprises an alignment bar and a lift bar. When the gates are closed, the alignment bars will engage the Opposite end of the suspension bars and bring them into proper alignment,

while the lift bars will be disposed'immediately under the ends of the suspension bars. When the unit is lifted, the suspension bars will rest in notches on the lift bars, and the load may be moved to a position over the multitiered rack and lowered. As the last tier of cathode assemblies engages the rack, a sensing member carried by the unit will engage assemblies in the uppermost tier and swing the gates to open position, where they will remain by gravity assist. The unit may then be lifted and returned to its original position at the assembly area, regardless of whether any or allof the next group of cathode assemblies has been placed on the slide rails.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of the unit of this invention, this figure also showing in part the configuration of the multi-tiered rack and the assembly station;

FIG. 2 is a top plan view of the unit of FIG. 1;

FIG. 3 is a front elevational view of the unit, showing in phantom lines the final positions of the cathode assemblies when lowered onto the multi-tiered rack; and

FIG. 4 is a fragmentary side elevational view of one end of one of the side gates showing the blade which holds the cathode assemblies in position when the unit.

is being located over the rack.

DESCRIPTION OF THE PREFERRED EMBODIMENT (FIG. 1). Flared guides 25 and 26 are provided for aiding the crane operator in positioning the hooks. I. The unit is intended to carry successive groups of cathode assemblies from an assembly station generally indicated in dot-dash lines at 27 in FIG. 1 to a multitiered rack generally indicated in dot-dash lines at 28. Although station 27 and rack 28 are shown in overlapping relation in FIG. 1, rack 28 will be located some distance away from station 27 on the plant floor, for example, directly behind station 27 as viewed in FIG. 1. Station 27 may be at the discharge end of a machine such as that shown in the aforementioned copending application and has a pair of spaced slide rails indicated in dot-dash lines at-29 on which the cathode assemblies are placed at, for example, one inch intervals. A cathode assembly is generally indicated in dot dash lines at 31 and comprises a thin sheet of copper 32 secured to a suspension bar 33 by a pair of copper straps 34, the

bar extending outwardly from both sides of the sheet and restingon rails 29. As described in greater detail in the aforementioned copending application, the as semblies 31 are moved-along the rails 29 by rotatable and reciprocable transfer bars 35 carrying fingers 36;

Legs 13 of unit 11 have hollow lower ends which may rest on pads 37 carried by frame 38 of station 27 outwardly of slide rails 29. Conical members 39 are mounted on pads 37 to aid in positioning legs 13 when unit 11 is lowered into position at station 27.

A pair of gates generally indicated at 41 and 42 are mounted on the opposite sides of unit 11, as seen in FIG. 3. Each side gate comprises an aligning bar 43 and a lifting bar 44. The aligning bars serve to align suspension bars 33 and retain them against lateral movement, while lifting bars 44 have notches 45 (FIG. 4) into which the ends of bars 33 will nestle as the unit is lifted.

Gates 41 and 42 are swingably mounted on legs 13 by bell cranks 46 and 47 respectively, and are of a length corresponding to the number of cathode assemblies 31 which it is desired to lift in each group. It will be noted that slide rails 29 may extend beyond gates 41 and 42. Gates 41 and 42 are swingable outwardly (to the left and right respectively in FIG. 3) from their lifting position shown in FIG. 3, and when in their open position will be clear of suspension bars 33. As the gates are swung inwardly, bars 43 will engage the ends of bars 33 and align them, and bars 44 will swing under the ends of bars 33 in position to lift them. It should be observed that when gates 41 and 42 are in their open position, they will be disposed outwardly of pivots 48 and 49 for bell cranks 46 and 47 respectively, and the weight of the gates will thus tend to hold them in their open position. When the gates are in their closed position and are lifting a group of cathode assemblies 31, the weight of the cathode assemblies will hold the gates in their closed positions so that the assemblies cannot escape or drop. I

Means are provided for swinging gates 41 and 42 to their closed positions after unit 11 has come to rest on pads 37. In the illustrated embodiment, this means comprises a pusher shown in dot-dash lines at 51 which is pivotally mounted on frame 38 of station 27 and is swingable by an actuator 52 in a counterclockwise direction as seen in FIG. 3. Pusher 51 has a portion engageable with a pin 53 on one of the bell cranks 47.

These bell cranks are linked to bell cranks 46 in such manner that swinging of bell cranks 47 counterclockwise in FIG. 3 will cause bell cranks 46 to swing clockwise, so that both gates will close. The linkage which connects bell cranks 46 and 47 comprises a rod 54 connected at one end to bell crank 47 and at the other end to a bell crank 55 mounted on frame 13 above bell crank 47. A rod 56 is connected at one end to bell crank 55 and at the other end to a bell crank 57 mounted on the opposite side of frame 12 above bell cranks 46. A rod 58 connects bell crank 57 to hell crank 46. I

Means are also provided for automatically opening gates 41 and 42 in the last stage of descent of unit 11 as cathode assemblies 31. are deposited on multi-tiered rack 28. This means comprises a sensing or contact member 59 in the form ofa flat bar (FIG. I) suspended below frame 12 by a pair of vertically sliding guides 60 and 61. Normally, member 59 will be suspended some distance below frame 12, as seen in FIG. 3. However, as unit 11 descends and thelowermost tier of cathode assemblies 31 is deposited on the lowermost rack tier, further descent of unit 11 will cause member 59 to engage the suspension bars 33 of the uppermost assembly tier and slide upwardly relative to the unit which continues to descend. A bell crank 62 is pivoted at 63 above bar 59 and is engageable by this bar so as to swing counterclockwise in FIG. 3. This will cause the bell crank to engage an abutment 64 carried by link 56, moving the latter to the left. This will cause bell crank 55 to swing counterclockwise and bell crank 57 to swing clockwise, opening gates 41 and 42. The latter at this point will, of course, not be supporting any assemblies, since they will have been deposited on rack 28.

In operation, let us assume an initial condition in which unit 11 is resting on pads 37 and gates 41 and 42 are in their open position. The crane having hooks 23 and 24 may be elsewhere at this time. Cathode assemblies 31 will be fed along slide rails 29 by fingers 36 with the relatively short spacing shown in FIG. 1. The sheet assemblies may be fed any distance along the slide rails, but normally the unit 11 will be utilized to pick up a group of sheet assemblies when they occupy the entire length of gates 41 and 42. For this purpose a limit switch (not shown) may be provided at the right hand end of the gates as shown in FIG. 1 which, when actuated by a cathode assembly 31 reaching this end, will stop further feeding of the cathode assemblies along the slide. rails until the group is lifted. This limit switch could also illuminate a signal lamp or other means of notifying the crane operator that the group of cathode sheets is ready to be lifted. The limit switch could further operate actuator 52 which will swing member 51 counterclockwise from its FIG. 3 position, engaging pin 53 and causing gates41 and 42 to swing inwardly. This will align all the suspension bars 33 which are at the same level on slide rails 29, and will position lifting bars 44 under the ends of the suspension bars. The crane operator will then engage hooks 23 and 24 on pins 21 and 22 respectively and lift unit 11 with the cathode assemblies. The ends of suspension bars 33 will be nestled in pockets 45 of lifting bars 44. It should be noted at this time that a blade 65 (FIG. 4) is secured to the right hand end of each aligning bar 43 as seen in FIG. 1 and extends inwardly therefrom so as to be disposed between the right hand suspension "bar 33 and the adjacent suspension bar. The purpose of these blades is to permit the crane operator to align his load with respect to the four tiers 66, 67, 68 and 69 of rack 28 by gently bumping the end suspension bar 33 against a stop on rack 28 indicated in dot-dash lines at 71 in FIG. 1. Blades 65 will prevent this bumping procedure from dislodging any of the suspension bars from pockets 45.

Unit 11 will then be lowered by the crane. As suspension bars 33 pass tier 66, one fourth of them will be stripped away from the rest at this level by rack 28 and the rest will continue to descend. When tier 67 is reached another fourth will be hung on the rack and so on until all four tiers are placed thereon.

Slight continued descent of unit 11 will cause member 59 to engage the uppermost tier of suspension bars and thus cause bell crank 62 to open gates 41 and 42 in the aforesaid manner. At this time no suspension bars will rest on bars 44 and the opening of the gates I will not be hampered. The gates will be held in their open position by their own weight. Unit 1 1 may then be lifted from the location of rack 28 and, with the gates still open, placed again on pads 37 in readiness for lifting another group of cathode sheets.

We claim:

1. In an apparatus for picking up, transporting and depositing a group of workpieces of the type having suspension bars from an assembly station to a rack, a rectangular frame, fixed legs depending from said frame, means at said assembly station supporting said legs, means onsaid frame engageable by a crane hook, a pair of side gates mounted on opposite-sides of said frame outwardly of said station and movable between an open position clear of said suspension bars and a closed lifting position, lifting bars on said gates disposed under the ends of said suspension bars when the gates are in their lifting position, selectively operable means for moving said gates from their open to their lifting position, said last-mentioned means being operable independently of said crane hook and said frame means engageable by the crane hook, means responsive to the weight of workpieces when the unit is lifted to hold said gates in their lifting position, and means responsive to lowering of said workpieces onto said rack for shifting and holding said gates in their open position, whereby the unit may be returned to a rest position at said station and left there without said crane.

2. The combination according to claim 1, further provided with coacting means on said unit and rack for properly locating-the workpieces with respect to the rack.

3. The combination according to claim 1, said means engageable by a crane hook comprising a pair of parallel 'members between which pins extend, said downwardly extending legs having hollow bottoms, and cone-shaped members at said station receivable by said hollow bottoms to properly locate the frame.

4. The combinationaccording to claim 3, further provided with flared. guides at opposite ends of said parallel frame members for said crane hooks.

5. The combination according to claim 1, said side gates being mounted on bell cranks pivoted to said legs, the gates being so positioned that they will be held in their open position by their own weight after being opened.

6. The combination according to claim 5, further provided with linkage means connecting said bell cranks whereby shifting one side gate to its lifting position will cause the other side gate to also move to its lifting position.

7. The combination according to claim 6, said linkage means comprising a pair of bell cranks pivoted on opposite sides of said frame above said sidegates, and rods connecting 'said bell cranks.

8. In an apparatus for picking up, transporting and depositing a group of workpieces of the type having suspension bars from anassembly station to a rack, a rectangular frame, legs, depending from said frame,

means at said assembly station supporting said legs,

means on said frame engageable by a crane hook, a pair of side gates mounted on opposite sides of said frame outwardly of said station-and movable between an open position clear of said suspension bars and a closed lifting postion, said side gates being mounted on bell cranks pivoted to said legs, the gates being so posi-- tioned that they will be heldin their open position by their own weight after beingopened, linkage means connecting said bell cranks whereby shifting one side gate to its lifting position will cause the other side gate to also move to its lifting position, said linkage means comprising a pair of bell cranks pivoted on opposite sides of said frame above said side gates and rods connecting said bell cranks, lifting bars on said gates dis- .posed under the ends of said suspension bars when the gates are in their lifting position, means for moving said gates from their open to their lifting position, means responsive to the weight of workpieces when the unit is lifted to hold said gates in their lifting position, means responsive to lowering of .said workpieces onto said to descend, and means connecting said last-named member to a rod connecting the two upper bell cranks.

9. In an apparatus for picking up, transporting and depositing a group of workpieces of the type having suspension bars from an assembly station to a rack, a rectangular frame, legs depending from said frame, means at said assembly station supporting said legs, means on said frame engageable by a crane hook, a pair of side gates mounted on opposite sides of said frame outwardly of said station and movable between an open position clear of said suspension bars and a closed lifting position, lifting bars on said gates disposed under the ends of said suspension bars when the gates are in their lifting position, means for moving said gates from their open totheir lifting position, means responsive to the weight of workpieces when the unit is lifted to hold said gates in their lifting position, means responsive to lowering of said workpieces onto said rack for shifting and holding said gates in their open position, whereby the unit may be returned to a rest position at said station and left there without said crane, said means responsive to the lowering of workpieces onto said rack for swinging said side gates to open position comprising a member movably mounted on said frame and engageable with the workpieces deposited on the rack as the frame continues to descend, and means linking said last-named member to said side gates.

10. In an apparatus for picking up, transporting and depositing agroup of workpieces of the type having suspension bars from an assembly station to a rack, a rectangular frame, legs depending from said frame, means at said assembly station supporting said legs, means on said frame engageable by a crane hook, a pair of side gates mounted on opposite sides of said frame outwardly of said station and movable between an open position clear of said suspension bars and a closed lifting position, lifting bars on said gates disposed under the ends of said suspension bars when the gates are in their lifting position, means for moving said gates from their open to their lifting position, means responsive to the weight of workpieces when the unit is lifted to hold said gates in their lifting position, means responsive to lowering of said workpieces onto said rack for shifting and holding said gates in their open position, whereby the unit may be returned to arest position at said station and left there without, said crane, the lifting bars of said gates having pockets for the reception of said suspension bars, and blades fixed to said gates immediately inwardly of the pockets at one end thereof,

whereby a suspension bar in said end pockets may be used to locate said workpieces horizontally with rement by one or more crane hooks, fixed legs extending downwardly from said frame'and straddling the suspension bars at said assembly station, pads at the assembly station engageable by said legs and having means for properly locating the frame with respect to the assembly station, a pair of gates on the opposite sides of and below said frame, said gates being mounted on said legs for movement between open positions in which they are clear of the suspension bars and lifting positions, each gate comprising an alignment bar disposed alongside the ends of the suspension bars and a lifting bar disposed below the suspension bars when in lifting position, said lifting bars having pockets for the reception of the suspension bar ends, means for simultaneously '8 moving said gates fromttheir open to lifting position, said last-mentioned means being operable independently of said crane hook and said frame means engageable by the crane hook, coacting means on said unit and rack for locating said workpieces with respect to the rack, means responsive to lifting of said apparatus with said workpieces by a crane for preventing opening of said gates, means responsive to continued descent of said unit over said rack after the workpieces have been deposited thereon for swinging said gates to their open position, and means holding said gates in their open position whereby the unit may be returned to the assembly station.

UNITED STATES PATENT OFFICE CERTIFICATE OF 'CGRRECTION Fahi & 9 Patent No. 3,792,391 w Dated T JTY 1 1974 Inventm-(s) Cass S. Kasper et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown b l Column 6, line 56, after "of" insert the ends of Signed and sealed this 1st day of October 1974.

(SEAL) Attest:

C. MARSHALL DANN MCCOY M. GIBSON JR. Attesting Officer Commissioner of Patents USCOMM- DC 60376-P59 u s covrnrmmn rnm'rmo OFFICE 930 FORM P040150 (10-69) 

1. In an apparatus for picking up, transporting and depositing a group of workpieces of the type having suspension bars from an assembly station to a rack, a rectangular frame, fixed legs depending from said frame, means at said assembly station supporting said legs, means on said frame engageable by a crane hook, a pair of side gates mounted on opposite sides of said frame outwardly of said station and movable between an open position clear of said suspension bars and a closed lifting position, lifting bars on said gates disposed under the ends of said suspension bars when the gates are in their lifting position, selectively operable means for moving said gates from their open to their lifting position, said last-mentioned means being operable independently of said crane hook and said frame means engageable by the crane hook, means responsive to the weight of workpieces when the unit is lifted to hold said gates in their lifting position, and means responsive to lowering of said workpieces onto said rack for shifting and holding said gates in their open position, whereby the unit may be returned to a rest position at said station and left there without said crane.
 2. The combination according to claim 1, further provided with coacting means on said unit and rack for properly locating the workpieces with respEct to the rack.
 3. The combination according to claim 1, said means engageable by a crane hook comprising a pair of parallel members between which pins extend, said downwardly extending legs having hollow bottoms, and cone-shaped members at said station receivable by said hollow bottoms to properly locate the frame.
 4. The combination according to claim 3, further provided with flared guides at opposite ends of said parallel frame members for said crane hooks.
 5. The combination according to claim 1, said side gates being mounted on bell cranks pivoted to said legs, the gates being so positioned that they will be held in their open position by their own weight after being opened.
 6. The combination according to claim 5, further provided with linkage means connecting said bell cranks whereby shifting one side gate to its lifting position will cause the other side gate to also move to its lifting position.
 7. The combination according to claim 6, said linkage means comprising a pair of bell cranks pivoted on opposite sides of said frame above said side gates, and rods connecting said bell cranks.
 8. In an apparatus for picking up, transporting and depositing a group of workpieces of the type having suspension bars from an assembly station to a rack, a rectangular frame, legs depending from said frame, means at said assembly station supporting said legs, means on said frame engageable by a crane hook, a pair of side gates mounted on opposite sides of said frame outwardly of said station and movable between an open position clear of said suspension bars and a closed lifting postion, said side gates being mounted on bell cranks pivoted to said legs, the gates being so positioned that they will be held in their open position by their own weight after being opened, linkage means connecting said bell cranks whereby shifting one side gate to its lifting position will cause the other side gate to also move to its lifting position, said linkage means comprising a pair of bell cranks pivoted on opposite sides of said frame above said side gates and rods connecting said bell cranks, lifting bars on said gates disposed under the ends of said suspension bars when the gates are in their lifting position, means for moving said gates from their open to their lifting position, means responsive to the weight of workpieces when the unit is lifted to hold said gates in their lifting position, means responsive to lowering of said workpieces onto said rack for shifting and holding said gates in their open position, whereby the unit may be returned to a rest position at said station and left there without said crane, said means responsive to the lowering of workpieces onto said rack for swinging said side gates to their open position comprising a member mounted for vertical movement on said frame and engageable with the workpieces resting on the rack as the frame continues to descend, and means connecting said last-named member to a rod connecting the two upper bell cranks.
 9. In an apparatus for picking up, transporting and depositing a group of workpieces of the type having suspension bars from an assembly station to a rack, a rectangular frame, legs depending from said frame, means at said assembly station supporting said legs, means on said frame engageable by a crane hook, a pair of side gates mounted on opposite sides of said frame outwardly of said station and movable between an open position clear of said suspension bars and a closed lifting position, lifting bars on said gates disposed under the ends of said suspension bars when the gates are in their lifting position, means for moving said gates from their open to their lifting position, means responsive to the weight of workpieces when the unit is lifted to hold said gates in their lifting position, means responsive to lowering of said workpieces onto said rack for shifting and holding said gates in their open position, whereby the unit may be returned to a rest position at said station and left there wIthout said crane, said means responsive to the lowering of workpieces onto said rack for swinging said side gates to open position comprising a member movably mounted on said frame and engageable with the workpieces deposited on the rack as the frame continues to descend, and means linking said last-named member to said side gates.
 10. In an apparatus for picking up, transporting and depositing a group of workpieces of the type having suspension bars from an assembly station to a rack, a rectangular frame, legs depending from said frame, means at said assembly station supporting said legs, means on said frame engageable by a crane hook, a pair of side gates mounted on opposite sides of said frame outwardly of said station and movable between an open position clear of said suspension bars and a closed lifting position, lifting bars on said gates disposed under the ends of said suspension bars when the gates are in their lifting position, means for moving said gates from their open to their lifting position, means responsive to the weight of workpieces when the unit is lifted to hold said gates in their lifting position, means responsive to lowering of said workpieces onto said rack for shifting and holding said gates in their open position, whereby the unit may be returned to a rest position at said station and left there without said crane, the lifting bars of said gates having pockets for the reception of said suspension bars, and blades fixed to said gates immediately inwardly of the pockets at one end thereof, whereby a suspension bar in said end pockets may be used to locate said workpieces horizontally with respect to said rack without being dislodged from said pockets by gently bumping a stop on the rack.
 11. In an apparatus for transporting workpieces such as cathode sheets having suspension bars from an assembly station in which the bars are relatively closely spaced and on the same level to a multi-tiered rack, a rectangular frame having central means for engagement by one or more crane hooks, fixed legs extending downwardly from said frame and straddling the suspension bars at said assembly station, pads at the assembly station engageable by said legs and having means for properly locating the frame with respect to the assembly station, a pair of gates on the opposite sides of and below said frame, said gates being mounted on said legs for movement between open positions in which they are clear of the suspension bars and lifting positions, each gate comprising an alignment bar disposed alongside the ends of the suspension bars and a lifting bar disposed below the suspension bars when in lifting position, said lifting bars having pockets for the reception of the suspension bar ends, means for simultaneously moving said gates from their open to lifting position, said last-mentioned means being operable independently of said crane hook and said frame means engageable by the crane hook, coacting means on said unit and rack for locating said workpieces with respect to the rack, means responsive to lifting of said apparatus with said workpieces by a crane for preventing opening of said gates, means responsive to continued descent of said unit over said rack after the workpieces have been deposited thereon for swinging said gates to their open position, and means holding said gates in their open position whereby the unit may be returned to the assembly station. 